Probability generating function for random variable

In summary, the conversation is about calculating the probability of a random variable X with probability generating function gX(s) = (5-4s2)-1. The conversation discusses calculating P(X=3) and P(X=4), and the use of g_X(s)=\sum P\{X=k\}s^k to find the probability. Ultimately, the conversation is not able to reach a conclusion and requires further clarification.
  • #1
tamintl
74
0

Homework Statement


A random variable X has probability generating function gX(s) = (5-4s2)-1

Calculate P(X=3) and P(X=4)

Homework Equations


The Attempt at a Solution


Ehh don't really know where to go with one... I know:

gX(s) = E(sx) = Ʃ p(X=k)(sk)

Nit sure how to proceed..
Any help would be great!

Regards
Tam
 
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  • #2
What is [itex]g_X(0)[/itex]?? What is [itex]g^\prime_X(0)[/itex]?? (the derivative)
 
  • #3
micromass said:
What is [itex]g_X(0)[/itex]?? What is [itex]g^\prime_X(0)[/itex]?? (the derivative)

[itex]g_X(0)[/itex] = 5-1= 1/5
[itex]g^\prime_X(0)[/itex]= 0
 
  • #4
Yes, and what if you calculate the same thing using

[tex]g_X(s)=\sum P\{X=k\}s^k[/tex]

??
 
  • #5
micromass said:
Yes, and what if you calculate the same thing using

[tex]g_X(s)=\sum P\{X=k\}s^k[/tex]

??

Not sure what u mean but [tex]g_X(0)=\sum P\{X=3\}0^3[/tex]=0 ?
Sorry
 
  • #6
tamintl said:
Not sure what you mean but [tex]g_X(0)=\sum P\{X=3\}0^3[/tex]=0 ?
Sorry

OK, if you have the series

[tex]P\{X=0\}+P\{X=1\}s+P\{X=2\}s^2+...[/tex]

what happens if I put s=0??
 
  • #7
micromass said:
OK, if you have the series

[tex]P\{X=0\}+P\{X=1\}s+P\{X=2\}s^2+...[/tex]

what happens if I put s=0??

You will get '0'
 
  • #8
tamintl said:
You will get '0'

No, you won't. Check again.
 
  • #9
I'm not sure.. Sorry
 

Related to Probability generating function for random variable

What is a probability generating function for a random variable?

A probability generating function (PGF) for a random variable is a mathematical function that encodes the probability distribution of the random variable. It is a useful tool for analyzing the behavior of a random variable and can be used to calculate various statistical quantities such as mean, variance, and higher moments.

How is a probability generating function different from a moment generating function?

While both a probability generating function and a moment generating function (MGF) are mathematical functions that describe the distribution of a random variable, they differ in the types of information they provide. A PGF encodes the probability distribution of a random variable, while an MGF encodes its moments (i.e. mean, variance, etc.). In general, PGFs are easier to work with, but MGFs can be used to derive PGFs.

What is the relationship between a probability generating function and a moment generating function?

The probability generating function and moment generating function are related through a transformation known as the inverse Laplace transform. Specifically, the PGF is the inverse Laplace transform of the MGF evaluated at -t, where t is a parameter. This relationship allows for converting between PGFs and MGFs.

How is a probability generating function used in probability theory?

In probability theory, a probability generating function is used to calculate the probability distribution of a random variable, as well as to derive various statistical quantities such as mean, variance, and higher moments. It is also useful for analyzing the behavior of a random variable and can be used in conjunction with other techniques, such as the Central Limit Theorem, to approximate the distribution of a sum of random variables.

Can a probability generating function be used for any type of random variable?

Yes, a probability generating function can be used for any type of discrete random variable, such as a binomial, Poisson, or geometric random variable. However, it cannot be used for continuous random variables, which require a different type of mathematical function known as a probability density function.

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